The Illusion of Mental Pictures - PowerPoint Presentation

Slide1

The Illusion of Mental Pictures

Zenon Pylyshyn

Rutgers University,

Center for Cognitive Science

http:/ruccs.rutgers.edu/faculty/pylyshyn.htmlSlide2

The illusion of mental pictures

There is no question that we (all but about 2% of us) experience mental images and, in some sense, use them to recall, anticipate and enjoy life in the absence of the things and people that we imagine.

Not only are we able to “picture” some object or scene in our “mind’s eye” but it seems that we

must

do so in order to solve certain kinds of problems.

Books are full of examples of how images helped people to make discoveries in science and create works of art – none of which would have happened without the capacity to use mental imagery. I will not rehearse all the examples, but they include Einstein,

Kikule

, …Slide3

The illusion about the causal role of mental pictures in thought

It is important that as scientists we consider what is assumed when we speak of creating, recalling and transforming mental images. Such tacit assumptions can be very damaging.

I have argued that there is a powerful illusion behind not only our folk understanding of mental imagery, but also behind our attempts to build scientific theories of it, and this illusion is not just a way of speaking or a handy metaphor. It is an essential part of our understanding of imagery. The very term “imagery” betrays an assumption about what it is like.

The illusion is that when we engage in what we call imaging or visualizing, there is, somewhere in our head,

something

that we see more or less the way we see the world, and which resembles a possible or actual visual scene about which we are thinking. Slide4

One common mistake in thinking about mental imagery

The

intentional

or

phenomenological fallacy

.

We are all inexorably drawn to confusing properties of the imagined world with properties of our image of it

.



Consider the power of this draw to the object, which

Wundt called the Stimulus Error.

Slide5

Intuitions about which property in the world maps onto the same property in its representation

Temperature, weight



Brightness



Shape, color



Relative location 

Relative orientation  (upside down?)

Size



Motion, speed 

Duration 

Metrical properties

 (distance?)

Metrical axioms, Euclidean properties

(

Pythagoras’ theorem

)Slide6

Imagine seeing these events unfolding…

You hit a baseball. What shape trajectory does it trace? It is coming towards you: Where would you run to catch it? If you have played baseball you would have a great deal of “tacit knowledge” of what to do in such well-studied cases.

You drop a rubber ball on the pavement. Tap a button every time it hits the ground and bounces. Plot bounce

height

vs

time.

Suppose you get

this pattern:

Drop a heavy steel ball at the same time as you drop a light ball

from, say, the leaning tower of Pisa. Indicate when they hit the ground. Repeat for different heights and weights.

(It turns out that people are Aristotelian rather than Galilean).

Examples to probe your intuition and your tacit knowledge

Time

since first

drop

height

What is responsible for

this pattern in your image?Slide7

What color do you see when two colored light beams overlap?

Two complementary colored light

beams => white

Two complementary colored filters or paint => black

?Slide8

Where would the water go if you poured into a full beaker full of sugar?

Is there conservation of volume in your image? If not, why not?Slide9

What do these image behaviors have in common?

Objects in your image do whatever you believe those objects would have done had you watched them under the same set of circumstances in reality.

Finding that your image mimics nature is not a discovery about images. It is a discovery about your tacit beliefs of what would happen in the world under conditions similar to those of the imagery experiment.Slide10

Aside: What can we conclude from the contents of conscious experience?

What is the status of

Tammet’s

description of how he does multiplication?

Is he lying about what he does, or is he just mistaken? Is there a correct answer?

Does his description constitute an explanation of how he multiplies? Slide11

That’s all I have to say about the status of conscious experience as a basis for building a scientific theory of mental processes – I hope it’s enough to raise some skepticism. I have more to say about this issue in my 2007 book;

Things and Places; How the mind connects with the world

MIT Press

(paperback 2010)Slide12

Representation of Space in Mental Images

This is the issue I am most interested in because it bears on some questions about how visual information is encoded as well as the vexing question of the role of conscious experience in cognitive science

The most interesting questions about

mental imagery

come

together in the problem of

representing spatial patternsSlide13

Spatial character of mental images

Some of the more impressive experimental results on mental imagery (mental rotation, mental scanning, mental size effects) appear to suggest that images

have spatial properties

(or ‘Images preserve metric spatial information’,

Kosslyn

, 1978).

One of the most explicit description of what the Picture Theory entails has been provided by Steve

Kosslyn

when he describes what he calls the depictive nature of mental images. Since it shows the intimate connection of images with spatial cognition I begin with this quote.Slide14

Images as depictive

representations

(Kosslyn, 1994, p 5)

“A depictive representation is a type of picture, which specifies the locations and values of configurations of points in a space. … In a depictive representation, not only is the shape of the represented parts immediately available to appropriate processes, but so is the shape of the empty space … Moreover, one cannot represent a shape in a depictive representation without also specifying a size and orientation….”

This is the claim that the

form

of representation of images

compels

certain properties to be represented. The reason for this assumption goes back to what “image” means to many people – and to the underlying

mental picture assumption

.Slide15

Images as displayed in “functional space”

“

The space in which the points appear need not be physical…, but can be like an array in a computer, which specifies spatial relations

purely functionally

. That is, the physical locations in the computer of each point in an array are not themselves arranged in an array;

it is only by virtue of how this information is ‘read’ and processed that it comes to function as if it were arranged into an array

(with some points being close, some far, some falling along a diagonal,

etc

).”

(

Kosslyn

, 1994, p5)

But it is important why the information is ‘read’ in one way rather than in another since that is what gives the account the appearance of being principled and explanatory.To understand why the picture theory does not offer an explanation one needs to understand the functional space proposal and it’s assumptions. Here are three examples.Slide16

What does being “spatial” entail?

Are images spatial? Do they

have

spatial properties such as

size, distance

, and relations such as

above, next-to, in-between

? Do the axioms of Euclidean geometry and measure theory hold of patterns displayed in them? e.g.,

Triangle Inequality:

ab

+ bc  ac and ab = ba

Pythagoras: If abc = 90°, then ab2 + bc2 = ac2If such axioms are true of images, what would that entail about how they must be instantiated in the brain?Could they be cortical space? What constraints does that entail?Is the space 2-D or 3D?Is there a coherent notion of a “functional space,” as something with the formal properties of space yet without being instantiated in real physical brain-space?

Images and space: some possible constraints

a

b

cSlide17

Example 1. Do images

have

(or just represent) size?

There are many studies showing that when subjects imagine something small it takes them longer to detect small features (e.g., a mouse’s whiskers) than when they imagine them as large. What does this tell us about the representation of size?

There are two possibilities: The “size” is either the size of the

image

on the retina or V1

* (*more later)

, or

it is the size of the thing imagined.

The first needs either a physical size or some still-unknown variables that obey the law

Time = Distance ÷ Speed. Notice that the equation does not describe a law that applies to a functional space.

The second can yield the observed result simply because people know what it would be like to view an object, namely if it is small the details will not be as clear or you will need to ‘zoom’ in on the object, to see the details. (Ask yourself: What if it were faster for the small image? What would you conclude?)Suppose, instead, the experiment asked you to report details in a large blurred or low-definition image as opposed to a small high definition image? Why do you predict that? Slide18

Example 2. One of the least controversial examples of image transformation: Mental rotation

Time to judge whether (a)-(b) or (b)-(c) are the same except for orientation increases linearly with the angle between them

(Shepard & Metzler, 1971) Slide19

What do you do to judge whether these two figures are the same shape?

When you make it rotate in your mind, does it seem to retain its rigid 3D shape without re-computing it?

Is this how the process looked to you?Slide20

The ‘obligatory’ constraint

The properties of shape rigidity and motion continuity and automaticity are the ones requiring explanation. They are the basis for postulating a functional space and a “rotation” operator. As philosopher Jesse

Prinz

puts it

(2002, p 118)

;

“If visual-image rotation uses a spatial medium [referred to as

functional space

], then images

must traverse intermediate positions

when they rotate from one position to another. A [symbolic] system can be designed to represent intermediate positions during rotation, but that is not obligatory.”

This is a very important observation to which I will return. But the statement is incomplete. It needs to answer the further question: What makes it obligatory that the object must ‘pass through intermediate positions’ when rotating in ‘functional space’, and what constitutes an ‘intermediate position’? These terms apply to the represented world

, not to the representation!Slide21

Aside on the parable of the mystery box

A Cognitive Scientist, out walking in a field, comes upon a black box which happens to have a meter and

recorder that records the meter’s changes over time.

The Cognitive Scientist examines lots of

records generated

by the box and finds the

pattern to

be quite systematic. It follows the following regular pattern:

Clarifying the Obligatory requirementSlide22

An illustrative example: Behavior of Mystery Box

Direction of tape motionSlide23

An illustrative example: Mystery Code Box

What does this behavior pattern tell us about the nature of the box?

Careful study reveals that pattern #2 only occurs in this special context when it is preceded by pattern ASlide24

The Moral:

Regularities in behavior may be due to either:

The inherent nature of the system or its structure or its

architecture

.

The content of

what the system represents

(what it “knows”).Slide25

The important distinction between architecture and represented content

It is only obligatory that a certain pattern must occur if the pattern is caused by fixed properties of the architecture as opposed to being due to properties of what is represented (i.e., what the observer

tacitly

knows about the behavior of that which is represented)

If it is obligatory only because the theorist says it is, then score that as a free empirical parameter (a wild card).

The important consequence is that if we allow one theory to stipulate what is obligatory without there being a principle that mandates it, then any other theory can stipulate the same thing. Such theories are unconstrained and explain nothing.

This failure of image theories is quite general – all picture theories suffer from the same lack of principled constraints.Slide26

How are these ‘obligatory’ constraints realized?

Image properties, such as size and

rigidity

are assumed to be inherent in the architecture (of the ‘display’)

That raises the question of

what kind of architecture could possibly enforce rigidity of shape?

Notice that neither a spatial display nor a

functional space

make it obligatory that shape be

rigidly

maintained as orientation is changed. Only certain physical properties can explain rigidity.Such rigidity could not be part of the architecture of an imagery system because we can easily imagine objects for which rigidity does not hold (e.g. imagine a rotating snake!).There is also evidence that ‘mental rotation’ is incremental, not holistic, and the speed of rotation depends on the conceptual complexity of the shape and the comparison task.Slide27

Example 3: Mental Scanning

Hundreds of experiments have now been done demonstrating that it takes longer to scan attention between places that are further apart in the imagined scene. In fact the time-distance relation is linear.

These have been reviewed and described in:

Denis, M., &

Kosslyn

, S. M. (1999). Scanning visual mental images: A window on the mind.

Cahiers de

Psychologie

Cognitive / Current Psychology of Cognition, 18

(4), 409-465.

Rarely cited are experiments by Liam

Bannon and me (described in Pylyshyn, 1981) which I will summarize for you.A window on the mind Slide28

Studies of mental scanning

Does it show that images

have

metrical space?

(Pylyshyn & Bannon. Described in Pylyshyn, 1981)

Conclusion: The image scanning effect is

Cognitively Penetrable

i.e.,

it depends on

Tacit Knowledge.Slide29

Studies of mental scanning

Does it show that images

have

metrical space?

(Pylyshyn & Bannon. Described in Pylyshyn, 1981)

Conclusion: The image scanning effect is

Cognitively Penetrable

i.e.,

it depends on

Tacit Knowledge.Slide30

What is assumed in the mental picture explanations of mental scanning?

In actual vision, it takes longer to scan a greater distance because real distance, real motion, and real time is involved, therefore this equation holds due to natural law:

Time

=

distance

speed

But what ensures that a corresponding relation holds in an image?

The obvious answer is: Because the image is laid out in real space!

But what if that option is closed for empirical reasons? Well you might appeal to a “Functional Space” which imagists liken to a matrix data structure in which some pairs of cells are closer and others further away, and to move from one to another it is natural that you pass through intermediate cells

Question: What makes these sorts of properties “natural” in a matrix data structure?

 The central problem with imagistic explanations…

Slide31

What warrants the ‘obligatory’ constraint?

To use

Prinz’s

term, it is not

obligatory

that the well-known relation between distance, speed and time hold in functional space or in a matrix. There is no natural law or principle that requires it. You

could

imagine an object moving instantly or according to any motion relation you like, and the functional space would then be made to comply with that since it has no constraints of its own.

So why is it natural to imagine a moving object traversing

intermediate empty space when getting from A to B?

Because that’s how real objects move through real space!Slide32

Why is it ‘natural’ to assume that functional space is like real space?

There are at least two possible reasons why a functional space, such as a matrix data structure, appears to have natural spatial properties (e.g., distances, size, empty places):

Because when we think of incarnations of functional space, such as a matrix, we think of how we picture them on paper.

In fact a matrix does not intrinsically have distance, empty places, direction or any other such property, except in the mind of the person who draws it or uses it!

Moving from one cell to another does not require passing through intermediate cells unless we stipulate that it does. A computer is quite happy to go directly from one cell to any other cell. The same goes for the very concept of ‘intermediate cell’.Slide33

Why is it ‘natural’ to assume a matrix …

Because when we think of a functional space, such as a matrix, we think of it as being a way of

simulating

real (cortical) space – making it more convenient to think about the consequences of the cortical space assumption.

This is why we think of some cells as being ‘between’ others, some being farther away, etc. This makes properties like distances seem natural because we interpret the matrix as standing in for real space.

In that case we are not appealing to a functional space in explaining the scanning effect, the size effect, etc.

The explanatory force of the explanation comes from the real space that we are assuming

.

This is just another way of assuming a real space (in the brain) where representations of objects are located in neural space.

We will see that all the reasons for the failure of the assumption that images are laid out on the surface of visual cortex apply equally to this ‘functional space.’Slide34

Functional space and explanatory power

There is a notion of explanatory power that needs to be kept in mind. It is best illustrated in terms of models that contain empirical parameters, as in fitting a polynomial curve to data.

The general fact about fitting a model to data is that the fewer parameters that need to be estimated from the data to be fitted, the more powerful the explanation. Thus the lower the order of the polynomial fit the better the explanation.

In terms of the current example of explaining results of experiments involving mental imagery, appealing to a “functional space” leaves open an indeterminate number of empirical parameters, so it provides a very weak (or vacuous) explanation.

A literal (brain) space, on the other hand, is highly constrained since it

must

conform to Euclidean axioms and Newtonian physics – otherwise it would not be the space of natural science. But that kind of space implies that images are displayed on a surface in the brain.Slide35

What next?

We turn now to the only way in which we might be able to explain the experimental imagery results in terms of pictorial properties, as assumed by picture theorists. That’s to locate the picture in the brain – because it is the only place where there is a literal physical space that could underwrite such operations as scanning or rotation or properties such as size or shape in the terms assumed by picture theorists.Slide36

What are some plausible reasons why we might find a mechanisms of imagery in visual cortex

There is neuroanatomical evidence for a

retinotopic

layout in the earliest visual area of the brain (V1).

Neural imaging data shows that V1 is more active during mental imagery than during other forms of thought.

Transcranial

magnetic stimulation (TMS) of visual areas interferes more with imagery than other forms of thought.

Clinical cases of visual

agnosia

show that some impairments of vision have associated impairments of imagery

(

Bisiach, Farah)Recent psychophysical observations of imagery show parallels with corresponding observations of vision, and these can be related in both cases to certain cells in V1 (e.g., oblique effect)

The good news for picture theoriesSlide37

Neuroscience evidence shows that the retinal pattern of activation is displayed on the surface of the cortex

Tootell, R. B., Silverman, M. S., Switkes, E., & de Valois, R. L. (1982). Deoxyglucose analysis of retinotopic organization in primate striate cortex.

Science, 218,

902-904.

There is a topographical projection of retinal activity on the visual cortex of the cat and monkey. Slide38

Drawing conclusions about the form of visual images from neuroscience data faces many hurdles

The capacity for imagery and for vision are independent.

All imagery results are observed in the blind

as well as in patients with no visual cortex. So there is nothing visual about them.

Cortical topography is 2-D, but

mental images are 3-D

– all phenomena (e.g. rotation) occur in depth as well as in the plane.

Patterns in the visual cortex are in retinal coordinates whereas

images are primarily in world-coordinates

Unless you make a special effort, your image of parts of the room stays fixed in room coordinates when you move your eyes or turn your head or walk around the room.

The bad

news for picture theoriesSlide39

…Problems with drawing conclusions about mental imagery from neuroscience data

Accessing and manipulating information in an image is very different from accessing it from the perceived world.

Order of access from images is highly constrained

.

Some have tried to explain this by postulating rapid decay of images, but the times involved in these demonstrations are not consistent with the data (e.g., times for reporting letters are comparable to those involving size or mental scanning).

Conceptual rather than graphical properties are relevant to image complexity (e.g., mental rotation) suggesting that image representations are conceptual.

If images consist in patterns on visual cortex then they behave differently when the same patterns are acquired from vision. For example the important

Emmert’s

law

applies to retinal and cortical images but not to mental images, a fact largely unnoticed.Slide40

…Problems with drawing conclusions about mental imagery from neuroscience data

The signature properties of vision (e.g., spontaneous 3D interpretation, automatic reversals, apparent motion, motion aftereffects, etc) are

absent in images

;

A cortical display account of most imagery findings is incompatible with the

cognitive penetrability of mental imagery

phenomena, such as scanning and image size effects;

The fact that the

Mind’s Eye

is so much like a real eye (e.g., oblique effect, resolution fall-off) should serve to warn us that we may be studying

what observers know about how the world looks

to them, rather than what form their images take (unless the Mind’s eye is exactly the same as the real eye!).

I will consider a possible neural explanation of the oblique effect later.Slide41

…Problems with drawing conclusions about mental imagery from neuroscience data

Many clinical cases cited by image theorists can be explained by appeal to tacit knowledge and attention

The ‘tunnel effect’ found in vision and imagery (Farah) is plausibly due to the patient knowing how things looked to her post-surgery (The experiments were done a year after).

Hemispatial

neglect seems to be an attention deficit, which explains the neglect in imagery reported by

Bisiach

. A recent study shows that image neglect does not appear if patients have their eyes closed (

Bartolomeo

&

Chokron

, 2002). This fits well with the account I have offered in which the spatial character of mental images derives from concurrently perceived space (I will give examples later).Slide42

A more detailed look at two examples where neuroscience evidence is used

Claims that fMRI and PET evidence supports the assumption that larger mental images have correspondingly larger regions of cortical excitation.

Claims that the Oblique Effect in imagery supports the assumption that images are laid out on the visual cortex.Slide43

1. Image size and the visual cortex

There is evidence that when imagining “large” objects that overflow one’s phenomenal image, a different pattern of activation in visual cortex occurs than when imagining a small object

.

This in itself is not remarkable since all scientists accept that a difference in mental experience must be accompanied by

some

difference in the neural state – this is called

the

supervenience

assumption:

no mental

differences without physical differences. This also follows from materialism.Slide44

Image size and neural encoding

In vision:

cells in the

parafoveal

area of the retina project onto the more frontal parts of the visual cortex. Thus when objects are large enough

so that they fall

onto the

parafovea

,

they will

activate frontal parts of the visual cortex.In imagery: it is claimed that imagining large objects (which fill the visual field) leads to increased activity in the frontal part of the visual cortex. Some have taken this as prima facie evidence that perceived (large) size is neurally encoded the same way as imagined (large) size.Slide45

Image size and the visual cortex…

But the explanation for why large

visual

objects activate more frontal parts of the visual cortex depends on the fact that fibers from

parafoveal

cells connect to these frontal areas.

This can’t be the case with mental images unless they are also on the retina

!

And anyway, how does the fact that large mental images activate frontal parts of the visual cortex explain why small details are easier to detect in large mental images? Or how does it explain why scanning across a large image takes longer just because it happens to lie in the more fontal visual cortex? All picture-theory explanations make essential reference to distances and sizes.

Many neuroscience explanations for imagery findings make exactly the same mistake of citing activation patterns that arise from connections to the retina, and which therefore do not work unless mental images are projected onto the retina. I will give just one more example of a such a neural explanation because the error in that case is particularly egregious.Slide46

2. The oblique effect and visual cortex

In vision, when a set of lines is to be discriminated (distinguished from a single blur) the discrimination is better when the lines are vertical or horizontal than when they are at a 45

°

angle. This is called the

Oblique Effect

. It is a low-level effect that occurs in the early vision module.

Does the Oblique effect occur with mental images?Slide47

Do images have low-level visual properties?

Imagine a grating in which the bars are:

Horizontal

Vertical

Oblique (45

°

)

Imagine the bars getting closer and closer together. In which of these displays do the bars blur together first?

In vision, the oblique bars blur sooner (called

oblique effect

)

In imagery, a similar result was reported by

Kosslyn et al.

(1)

(2)

(3)Slide48

Neurological explanations for both cases?

An accepted explanation of the psychophysical case (where lines are seen) is that

in primary visual cortex (V1) there

are more cells tuned to horizontal and vertical orientations than to oblique orientations, so horizontal and vertical discrimination is more sensitive. Can this fact also explain why imagined bars show the same pattern?

Kosslyn

et al claim that it does and that this provides further support for the view that images are laid out in visual cortex.

But this argument rests on a misunderstanding of how the orientation-specific cells are tuned to specific orientations: the tuning comes from the way they are connected to photoreceptive cells on the retina.

Vertical cells

are more often connected to columns of photocells while

horizontal cells

are more often connected to rows of photocells (relative to the retina).Slide49

Neurological explanations for both cases?

If patterns of bars were activated on the surface of cortex by mental imagery, as assumed by picture-theorists, then no overall bias toward vertical-horizontal bars would occur. Horizontal cells would be no more likely to be activated by horizontal patterns

on the surface of the visual cortex

than by vertical patterns. The only way that images of horizontal bars would preferentially activate horizontal cells is if the images were on the retina!Slide50

What happens when horizontal/vertical cells are activated by means other than retinal patterns?

9 vertical

9 horizontal

5 oblique

The proportion of Vertical, Horizontal & Oblique cells remains the same in all cases – they are

located at random on the surface of visual cortex!Slide51

An overarching consideration:

What if colored three-dimensional images were found in visual cortex? What would that tell you about the role of mental images in reasoning?

Would this require a homunculus?Slide52

Should we welcome back the homunculus?

In the limit if the visual cortex mapped the contents of one’s conscious images we would need an interpreter to “see” this display in visual cortex

But we will never have to face this prospect because experiments show that the contents of mental images are already

conceptual

(or, as Kosslyn puts it, are ‘predigested’) and therefore unlike any picture.

Finally, you can make your image do whatever you want, and to have whatever properties you wish.

There are no known constraints on mental images that cannot be attributed to lack of knowledge of the imagined situation (e.g., imagining a 4-dimensional object).

Slide53

What is the alternative to a picture in V1

Even accepting the tacit knowledge explanation of the scanning result, there remains an open question: How is the right amount of time computed in the scanning experiment. I don’t claim that observers just stand by idly until the right amount of time has passed and then click the button indicating that the scan has reached its goal (even though psychophysical studies show that they are capable of doing so).

I think there is something to the scanning explanation, except that the space being scanned is not in the head but in the concurrently perceived real space.Slide54

Are there any ways of representing spatial layouts that are possible, given these problems?

Maybe we have been looking in the wrong place for things that fall under the formal requirements of being spatial. Maybe they are not in the head after all.

I have sketched a way of looking at this problem that locates the spatial character of thought in the concurrently-perceived world (see Chapter 5 of

Things and Places

). I will end with just a hint of this approach. It relies on findings from the study of the interaction among perceptual modalities and imagery as well as with motor actions and also neuroscience findings concerned with coordinate transformation mechanisms in the brain.Slide55

Another chapter in the imagery debate:

The relation

of images to vision and motor control

It has always seemed to me that one of the properties of mental images that makes them appear spatial is that they connect in certain ways not only with vision, but also with the motor system:

We can point to things in our image

!

<example>

We can “project” our images onto perceived space – even space perceived in different modalities. I believe that this observation is the key to the spatial character of images.

This projection does not require a picture to be projected, only the location of a small number of features. Over the past few decades I have been studying a mechanism called a visual index, or a FINST, that is well suited for this task.Slide56

What about mental scanning?Slide57

Using a concurrently perceived room to anchor

FINST

s tagged with map labelsSlide58

Studies of mental scanning

Does it show that images

have

metrical space?

The image scanning effect was shown to be Cognitively Penetrable

.

But what allows a smooth scan across the image is the perceptual display. Without the perceived map scanning would not be smooth and continuous and the timing would not be accurate

(Pylyshyn & Cohen, 1999).Slide59

Where do we stand?

It seems that a literal picture-in-the-brain theory is untenable for many reasons – including the major empirical differences between mental images and cortical images. A serious problem with any format-based explanation of mental imagery is the cognitive penetrability of many of the imagery demonstrations.

The pictorial quality of images may be an illusion that arises from the similarity of the experience of imaging and of seeing

So how do we explain the similarity of the experience

of imagining and of seeing – the fact that they both

seem to involve a pictorial panoramic display?

It is very likely that neither experience directly reveals

the form of the representation.Slide60

Neuroscience evidence shows that the retinal pattern of activation is displayed on the surface of the cortex

Tootell, R. B., Silverman, M. S., Switkes, E., & de Valois, R. L. (1982). Deoxyglucose analysis of retinotopic organization in primate striate cortex.

Science, 218,

902-904.

There is a topographical projection of retinal activity on the visual cortex of the cat and monkey. Slide61

Conscious experience and the picture-theory

The picture theory was initially meant to explain why our perceptual experience is panoramic and stable while the visual inputs are partial and changing. This assumes that the

content of experience

is represented.

But the picture theory of vision has been thoroughly

discredited: There is no rich panoramic display in vision

(e.g., see change blindness, superposition studies, …)Slide62

This is what our conscious experience suggests goes on in vision…Slide63

This is what the demands of explanation suggests must be going on in vision…Slide64

For a copy of these slides see:

http://ruccs.rutgers.edu/faculty/pylyshyn/ImageryClass2011/YaleTalk.pptx

For a copy of these slides see:

For a copy of these slides see:Slide65

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